Protocol Buffers are a flexible method for handling serialized data, generally for use with a database. Google has been using them internally for some time, and has now made it available for all to use. You can examine the documentation and download the package from Google.

The documentation is very detailed and is actually pretty interesting reading. It also shows that Protocol Buffers were created to fit a specific need within Google. I think that they are bound to appeal to anyone who has struggled with fitting XML into this particular type of application.